Searching for Ultra High Energy Searching for Ultra High Energy Neutrinos with ANITA and SalSANeutrinos with ANITA and SalSA

Amy Connolly for the ANITA andSALSA Collaborations

TeV Particle Astrophysics13-15 July 2005

Motivation:Motivation:The GZK The GZK ProcessProcess

Greisen-Zatsepin-Kuzmin: Cosmic rays >1019.5 eV from sources > 50 Mpc should not be detectable

Flu

x ×

E3 /

1024

(eV

2 m

-2 s

-1 s

r-1)

log10(E) (eV)

0.1

0

1.0

18 19 20 2117

Yet: ~20 events observed >1019.5 eV

Do not definitively point to any “local” known object(s)

Do not expect significant bending in intergalactic fields at these momenta.

~

Expect neutrino flux in the UHE region: An important piece of the GZK puzzle.

Motivation (cont):Motivation (cont):Only useful messengers >100 TeV: Only useful messengers >100 TeV: ’s’s

• Photons lost above 30TeV: pair production on IR & wave background

• Protons & Nuclei: scattered by B-fields or

GZK process at all energies

• But the sources extend to 1021 eV

Every new energy band yields major discoveries

at

tenu

atio

n le

ngth

(M

egap

arse

cs)

scale size of Local Group

domain of neutrinodominance

IR,CMB,URB ! e+ + e-

Beyond kmBeyond km33-Scale Detection Volume-Scale Detection Volume

Ice Cube ANITA SalSA

Atten. length >100 m ~km ~km

Threshold > 1 TeV 1018 eV 1017 eV

Sensors 4800 PMT’s

~40 antennas

~1000 antennas

[V]eff (w.e.) 1 km3 sr ~ 104 km3 sr ~102 km3 sr

Livetime years weeks years

Rate of UHE cosmic rays is ~1/km2/ century

8 km

Antarctica Isacksen salt dome

Ellef Ringnes Island, Canada1400 km

Idea by Gurgen Askaryan (1962)Idea by Gurgen Askaryan (1962)

lead

UHE particle

Macroscopic size: RMoliere ≈ 10 cm, L ~ meters

Bremsstrahlung: e- → e-

Pair Production: → e+e-

→ EM Shower

• A 20% charge asymmetry develops: – Compton scattering: + e-(at rest) + e-

– Positron annihilation: e+ + e-(at rest) + • Excess moving with v > c/n in matter

→ Cherenkov Radiation dP d• If >> L → COHERENT EMISSION P ~ N2

> L → RADIO/MICROWAVE EMISSION

~

This effect was confirmed experimentally by Gorham, Saltzberg at SLAC in 2002

Long Attenuation Lengths in Long Attenuation Lengths in Radio in Ice, Salt, SandRadio in Ice, Salt, Sand

South Pole Ice

1 km

Hockley Mine near Houston, TX

The GLUE experiment sought UHE neutrinos by observing the moon’s regolith.

ANITA ANITA (ANtarctic Impulsive Transient Antenna)(ANtarctic Impulsive Transient Antenna)

Each flight ~15 days –

or more

40 quad-ridged horn antennas, dual-polarization, with 10± cant

Downgoing - not seen by payloadUpcoming – absorbed in the earth

! ANITA sees “skimmers”.

ANITA-lite 2003-2004ANITA-lite 2003-2004• Practice run with 2 antennas –

piggybacked on TIGER • 18 day flight• Virtually every subsystem

planned for ANITA tested • Calibration pulses sent to

payload from ~200 km away

• Measured level of emission consistent with Galactic+Solar+kTice. Spectrum also consistent with quiet sun model

Angular resolution measured:ANITA-lite: t)=0.16 ns ! =2.3±

ANITA: expect t)=0.1 ns → =1.5°, =0.5°

Will show limits from ANITA-lite

Anita SimulationAnita Simulation• Ray tracing through ice, firn (packed snow near

surface)• Fresnel coefficients• Attenuation lengths are depth and

frequency dependent• Include surface slope and roughness• 40 quad ridged horn antennas arranged in 4 layers• Bandwidth: 200 MHz-1200 MHz• For now, signal in frequency domain• Measured antenna response• Secondary interactions included• Weighting accounts for neutrino attenuation through

Earth, etc.

ice

[S. Barwick]

Complementary simulations being developed – essential!

Reflected RaysReflected RaysWork by: S. Barwick, F. Wu from University of California at Irvine

TIR

Micro-black holes at ANITA Energies

• Could measure cross section from relative rates of direct (far) to reflected (near).

[S. Barwick]

[S. Barwick &F. Wu]

• ANITA could (possibly) detect events where a signal is reflected from ice-bedrock interface

• Signals suffer from extra attenuation through ice and losses at reflection • At SM ’s, reflected rays not significant

• At large cross-sections, short pathlengths → down-going neutrinos dominate ! reflected rays important

SM

10 100 10001

Direct rays

Reflected rays

Uncertainty at ice-bedrock interface being investigated: under-ice topologies, radar reflectivities, use Brealt code to study interfaces quantitatively

SkymapsSkymapsFor each balloon position:

After a complete trip around the continent, cover all Right Ascensions

If we could observe reflected rays, could view more sky!

10% reflected power

SalSA (Saltdome Shower Array)SalSA (Saltdome Shower Array)

Auger: Tau neutrino decay events

~1 GZK event per year?

SalSA sensitivity, 3 yrs live

70-230 GZK neutrino events

• ANITA sensitivity, 45 days:~5 to 30 GZK neutrinos

IceCube: high energy cascades

~1.5-3 GZK events in 3 years

A large sample of GZK neutrinos using radio antennas in a 12£ 12 array of boreholes in natural Salt Domes

SalSA simulations being developed, building on experience modeling GLUE, ANITA

SalSA Angular ResolutionSalSA Angular ResolutionWork by: P. Gorham, University of Hawaii and Kevin Reil, SLAC

[P. Gorham]

• Performed chi-squared analysis from two hadronic shower event types – Fully contained – Parallel to a face 250 m

outside array• Fit to

– Amplitude of Cerenkov signal

– Polarization• At 8£1016 eV:

– Contained: fraction of deg.– Non-contained: ~1 deg.

• Improves with energy

SalSA Cross Section MeasurementSalSA Cross Section Measurement

Use Poisson likelihood

cross section can be measured

from distribution

At SM , only 10% of events in sensitive region

Generate distribution from simulation and throw dice for many pseudo-experiments

For experiments w/ 100 events

With 300 events

@1018 eV,

Binning: ~2±

N

cos

<Lmeasint>=400 § 130 km

Salt Dome Selection:Salt Dome Selection:U.S. Gulf Coast Most PromisingU.S. Gulf Coast Most Promising

• Studying surveys from 70’s, 80’s for Nuclear Waste Repository sites– Requirements have large

overlap with SalSA, large, stable dome, near surface, with dry salt, no economic usage

– Strong candidates:• Richdon (MS), Vacherie

(LA), Keechie (TX)– We are visiting dome sites to

explore feasibility of SalSA given local geography, infrastructure, politics

Houston New OrleansHockley salt Dome & mine

Salt origin: Shallow Jurassic period sea, 200-150M yrs old, inshore Gulf coast area dried ~150 Myrs ago

Plasticity at 10-15km depth leads to ‘diapirism’ : formation of buoyant extrusions toward surface

! Stable salt diapirs all over Gulf coast

SensitivitiesSensitivities

• SalSA & ANITA– SalSA lower threshold – ANITA higher V,

shorter livetime• Two independent

simulations for each experiment give similar results for ES&S “baseline”– ANITA: handful of

events – SalSA: ~13

events/year

SalSA1 year

ANITA RoadmapANITA Roadmap• ANITA-lite PRL coming soon• ANITA EM flight this summer• First ANITA flight 2006-2007 Austral summer

SalSA Roadmap (In Tandem)SalSA Roadmap (In Tandem)• Select 3-5 salt domes, drill a few holes

• Use chemical & loss-tangent measurements on core, plus borehole radar to assess initial salt quality

• Choose best of initial domes that meet requirements for three or four deep (3km) boreholes, to install a ‘Salsita’ (4 holes)

• 1-2 years’ operations to establish proof-of-concept, and discover or confirm small sample of GZK neutrino events, then propose full array

Salsita could be contemporary with ANITA, Auger, IceCube

Backup Slides

Validating our Simulations (cont)

[P. Gorham]

[S. Hoover]

ANITAProjection of Askaryan signal onto the sky:

SalSA: Benchmark Detector Parameters

• Overburden: 500 m • Detector

– Array starts at 750 m below surface – 10 x 10 string square array, 250 m horiz. separation – 2000 m deep, 12 “nodes”/string, 182 m vert. separation– 12 antennas/node

• Salt extends many atten. lengths from detector walls• Attenuation length: 250 m• Alternating vert., horiz. polarization antennas• Bandwidth: 100-300 MHz• Trigger requires 5/12 antennas on node, 5 nodes to fire:

Vsignal>2.8 £ VRMS

• Index of refraction=2.45• Syst. Temp=450K=300K (salt) + 150K (receiver)

Impact of Salt Properties

• Track length L– X0

ice=43 cm, X0salt=10.3 cm ! Expect

Lsalt/Lice=0.26. Simulations show 0.34.

• Cerenkov index of refraction factor

• Cerenkov threshold

• Critical energy

• Coherence

• Angular scaling

Secondary Interactions• Generate from

MMC for each flavor, interaction type

• From MMC, also retrieve multiplicity of each type of sec. interaction

• Force neutrinos in our simulation to obey these distributions

• For now, consider interaction (primary or secondary) which contributes the strongest signal

• Critical for flavor ID

Example Probability Distribution from MMC for muon brem. showers

P. Miocinovic

Anita – Ice PropertiesAnita – Ice PropertiesUse measured ice and crust layer thicknesses (model is Crust 2.0 based on seismic data)

Use measured attenuation lengths (frequency dependent)

Rays traced in ice with depth-dependentindex of refraction.

n(z): 1.8 in deep ice 1.3 at surface

Temperature-dependence also included: ~few hundred m in warmest ice (in firn and near bedrock) ~1300 m at mid-depth

[D. Besson]

[P. Gorham]